Combine all of the measured ingredients in a small bowl and season with salt and pepper; set aside.

For the sandwich:

Place the oil and vinegar in a medium, nonreactive bowl and whisk to combine. Add the onions, season with salt and pepper, and stir to coat. Set aside until the onions mellow in flavor, about 10 minutes. Meanwhile, lightly toast the pitas and set aside.When the onions are ready, add the cucumbers to the bowl and toss until coated with the vinaigrette.

Spread about 1 heaping tablespoon of the yogurt sauce inside each pita.Place a quarter of the lamb and a quarter of the cucumber-onion mixture in each of the pitas. Drizzle the desired amount of remaining sauce over the tops of each pita and serve.* Some larger grocery/specialty stores sell this precooked and sliced and is used to make Gyros.